The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
An airplane is driven by several jet engines each housed in a nacelle also harboring an assembly of ancillary actuation devices related to its operation and ensuring various functions when the jet engine is operating or at a standstill.
These ancillary actuation devices notably comprise a thrust reversal mechanical system and a nozzle variation system.
The role of a thrust reverser upon landing of an airplane, is to improve the braking capability of the latter by redirecting towards the front at least one portion of the thrust generated by the jet engine. In this phase, the reverser gives the possibility of sending towards the front of the nacelle all or part of the gas flows ejected by the jet engine, consequently generating a counter-thrust which will be added to the braking of the wheels of the aircraft. To do this, a thrust reverser comprises on either side of the nacelle a mobile cowl which may be displaced from a deployed position which opens in the nacelle a passage intended for the deflected flow during a braking phase on the one hand and a retracted position which closes this passage during normal operation of the jet engine or when the airplane is at a standstill on the other hand.
The mobile cowls may fulfill a deflection function or simply a function for activating other deflection means.
In the case of a reverser with deflection grids, reorientation of the airflow is carried out by deflection grids, associated with reversal flaps which block a portion of the air circulation vein, the cowl only having a simple sliding function aiming at exposing or covering these deflection grids.
Moreover, in addition to its thrust reversal function, the sliding cowl belongs to the rear section and has a downstream side forming the ejection nozzle aiming at channeling the ejection of the air flows.
The optimum cross-section of the ejection nozzle may be adapted depending on the different flight phases, i.e. take-off, ascent, cruising, descent phases.
It should be noted that the operating phases of the variable nozzle and of the thrust reverser are distinct, the variable nozzle can only operate when the reverser is activated upon landing.
According to known devices, the variable nozzle may be made from one or several dedicated mobile elements, such as pivoting flaps or a translatable cowl portion or this function may be fulfilled by the mobile cowl itself by translational movements of small amplitude not activating the thrust reversal function.
For an extensive and detailed description of different embodiments, reference may be made to documents FR 2 922 058, FR 2 902 839, FR 2 922 059, inter alia.
In order to allow the driving of the mobile cowl in its thrust reversal function and the driving of the variable nozzle, it should generally be resorted to dedicated simple effect actuators, or to dual action actuators having a dual rod.
Document GB 2,446,441 describes a control architecture for a jet engine nacelle comprising a thrust reversal device associated with a variable nozzle device. The system described in document GB 2,446,441 uses dual action actuators.
For reasons of size and of mass of the nacelle, it should ideally be possible to use simple action actuators in order to apply both functions.
One of the problems posed by the application of simple action actuators for controlling both devices or functionalities is the observance of aeronautical safety standards and more particularly criteria for control segregation for the thrust reversal device and availability criteria for the variable nozzle device.
For a thrust reversal device with a hydraulic control as they for example exist on the A340, each mobile cowl is associated with, on the one hand, two so-called primary locks installed on the upper and lower actuators, the control of which by a hydraulic action is allowed by joint driving of two valves for closing the hydraulic supply circuit of the actuators, and, on the other hand, with a tertiary lock with an independent electric drive.
For safety reasons, the driving operations of both valves and of the tertiary lock should be performed along perfectly segregated control lines.